Field of the Invention
Embodiments of the invention relate generally to the field of memory devices and more particularly, to reducing leakage currents and discharging power in a voltage generator circuit of a memory device.
Description of the Related Art
Flash memory is a non-volatile memory that can be electrically erased and reprogrammed. It is primarily used in memory cards, USB flash drives, and the like for storage of data in computer systems. Generally, flash memory stores information on an array of floating gate transistors, called “cells”, each of which traditionally stores one bit of information. Each cell is characterized by a threshold voltage (Vt). By adding or removing charge from a floating gate, the threshold voltage of the cell changes, thereby defining whether the cell is programmed or erased. The threshold voltage level indicates the value for a single bit of information, generally represented as a 1 or 0. Multi-level cells may include more than two ranges that are representative of additional values, such as two or more bits of information. In memory cells, the voltages supplied include program verify voltages, read voltages, erase voltages, and the like. A memory device generally includes one or more voltage sources that provide these and other voltages to the cells of the memory array and/or to other locations within the memory device. In certain configurations, the supplied voltages are provided by internal voltage generators that are connected to transistors that make up the cells. For instance, each memory device can include multiple voltage generators that are configured to output a voltage for the program, read and verify operations.
To generate high voltages (e.g., voltages above a common voltage (Vcc)), such as program and erase voltages, the voltage generators often employ a charge pump circuit that is capable of supplying the desired voltage levels. The high voltage power output from the charge pump circuit is transferred to other locations in the flash memory via high-voltage switching circuits (HV switching circuits). Unfortunately, during periods when the charge pump circuit is not operating, the stand-by current of the charge pump circuit may leak to a lower-potential node. This may be referred to as a leakage current. For example, a leakage current can flow from the charge pump circuit through the HV switching circuit. Further, when the charge pump circuit is not operating, it may be desirable that charges remaining at nodes within the voltage generator be discharged. Discharging may avoid overstressing a cell with a voltage that could otherwise remain on the output lines.
Embodiments of the present invention may be directed to one or more of the problems set forth above.